The eye 



ts^ 



the inner molecuiax layer, within which they terminate in arboriza- 

 tions. 



3. Inner Molecular (Inner Plexiform) Layer. — This layer consists 

 of the arborizations of the dendrites of (i) the cells of the ganglionic 

 layer, and (2) the bipolar cells of the inner nuclear layer. The 

 intercommunications between these two sets of dendrites give rise 

 to five strata, according to Ramon y Cajal. Besides these, there are 

 the arborizations of the processes of the spongioblasts of the inner 

 nuclear layer, which are likewise arranged in strata. 



4. Inner Nuclear or Granular Layer. — ^This layer consists of ceUs 

 which are arranged in three groups, namely, (i) bipolar cells, 

 (a) horizontal cells, and (3) spongioblasts, or amacrine cells. The 



Fig. 635. — Scheme of the Horizontal Cells and Spongioblasts of 

 THE Retina (Ramon y Cajal). 



A. Rod-fibres ' 2. Inner Molecular Layer 



B. Cone-fibres /,r, A, ) Spongioblasts extending to 

 I. Outer Molecular Laj-er j, L f different depths 



a, b. Horizontal Cells, with arborizations M(, n. Spongioblasts with diffuse processes 



c. Horizontal Cell, with deep processes o. Ganglionic Nerve-cell 



bipolar cells are the most numerous, and are nucleated. Each cell 

 gives off two processes — internal and external. The internal 

 processes of the cells enter the inner molecular layer, and terminate 

 at different levels in arborizations. The external processes pass 

 into the outer molecular layer, and terminate in arborizations in its 

 outermost part, which are closely related to the terminal parts 

 of the rods and cones of the bacillary layer. According to Cajal, 

 the bipolar cells are of two kinds— rod-bipolars and cone-bipolars. 

 The external processes of the rod-bipolars ramify around the ter- 

 minal parts of the rod-fibres, and the internal processes arborize 

 around the cells of the ganglionic layer. The external processes of 

 the cone-bipolars form horizontal arborizations aroimd the terminal 



96 



